Animation. Why use motion? Volume rendering [Lacroute 95] Cone Trees [Robertson 91]

Transcription

1 CS448B :: 1 Nov 2011 Animation Why use motion? Visual variable to encode data Direct attention Understand system dynamics (?) Understand state transition Increase engagement Jeffrey Heer Stanford University Cone Trees [Robertson 91] Volume rendering [Lacroute 95] Video Video 1

2 NameVoyager [Wattenberg 04] Topics Motion perception Principles for animation Animation to convey process/dynamics Animated transitions Perceiving Animation Motion Perception Under what conditions does a sequence of static images give rise to motion perception? Smooth motion perceived at ~10 frames/second (100 ms). 2

3 Motion as a visual cue Segment by Common Fate Pre-attentive, stronger than color, shape, More sensitive to motion at periphery Similar motions perceived as a group Motion parallax provide 3D cue (like stereopsis) Tracking Multiple Targets Grouped dots count as 1 object How many dots can we simultaneously track? ~4-6. Difficulty increases sig. at 6. [Yantis 92, Pylyshn 88, Cavanagh 05] Dots moving together are grouped 3

4 Grouping based on biological motion Motions show transitions See change from one state to next [Johansson 73] start Motions show transitions See change from one state to next Motions show transitions See change from one state to next Shows transition better, but Still may be too fast, or too slow Too many objects may move at once end start end 4

5 Velocity Perception Intuitive physics [Kaiser 92] What is perceived as smooth, uniform motion? Velocity perception can be affected by: Path curvature Size / depth perception Luminance contrast (DEMO) Intuitive physics [Kaiser 92] What is motion if string cut at nadir of motion? Intuitive physics [Kaiser 92] Seeing dynamic motion improves performance What is motion if string cut at apex of motion? 5

6 Constructing Narratives Attribution of causality [Michotte 46] Attribution of causality [Michotte 46] Animation Helps? Hurts? Attention Adirect attention Adistraction Object ConstancyAchange tracking Afalse relations Causality Engagement Acause and effectafalse agency Aincrease interesta chart junk Calibration A Atoo slow: boring Atoo fast: errors [Reprint from Ware 04] 6

7 Principles for Animation Principles for Animation Character Animation (Johnston & Thomas 81, Lasseter 87) Squash and stretch Exaggeration Anticipation, Follow-through Staging, Overlapping Action Slow-in / Slow-out Squash and stretch Defines rigidity of material Should maintain constant volume Staging Clear presentation of one idea at a time Highlight important actions Lead viewers eyes to the action Motion in still scene, stillness in busy scene Motion clearest at silhouette Smoothes fast motion, similar to motion blur 7

8 Anticipation Show preparation for an action Follow-through Emphasize termination of action Slow-in, slow-out Example: Andre and Wally B. Space in-betweens to provide slow-in and out Linear interpolation is less pleasing 8

9 Example: Andre and Wally B. Example: Andre and Wally B. Example: Andre and Wally B. Principles for Animation Animated Presentations (Zongker & Salesin 03) Make all movement meaningful Avoid squash-and-stretch, exaggeration Use anticipation and staging Do one thing at a time 9

10 Principles for animated presentations [Zongker 03] Make all movement meaningful Avoid squash and stretch, exaggeration, etc. Highlight important things in simple ways Avoid instantaneous changes Reinforce hierarchical structure with transitions Smoothly expand and compress detail Reinforce animation with narration Distinguish dynamics from transitions Do one thing at a time Principles for conveying information Congruence Expressiveness? The structure and content of the external representation should correspond to the desired structure and content of the internal representation. Apprehension Effectiveness? The structure and content of the external representation should be readily and accurately perceived and comprehended. [from Tversky 02] How does it work? Convey Process and Dynamics 10

11 Animation: Can It Facilitate? Tversky et al reviewed studies in animation for conveying dynamic processes. Where benefits were found, the comparison was often unfair: the information was not equivalent In other cases, no difference in learning Implications: Comparisons of static and animated displays should use displays with equivalent information Static sequence may be as good or better Problems understanding animation [Tversky] Difficult to estimate paths and trajectories Motion is fleeting and transient Cannot simultaneously attend to multiple motions Parse motion into events, actions and behaviors Misunderstanding and wrongly inferring causality Anthropomorphizing physical motion may cause confusion or lead to incorrect conclusions Break into static steps Break into static steps Two-cylinder Stirling engine Two-cylinder Stirling engine 11

12 Challenges Choosing the set of steps How to segment process into steps? Steps often shown sequentially for clarity, rather than showing everything simultaneously Administrivia Tversky suggests Coarse level segment based on objects Finer level segment based on actions Static depictions often omit finer level segmentation Resource: Understanding Comics by Scott McCloud Assign 3: Interactive Visualization Create an interactive visualization application. Choose a data domain and select an appropriate visualization technique. 1. Choose a data set and storyboard your interface 2. Implement the interface using tools of your choice 3. Submit your application and produce a final write-up You may work individually or in groups of 2. Due by end of day on Tuesday, November 1 Next Lecture: Design Crits We will be having peer design critiques in class. Come prepared to constructively analyze the strengths and redesign opportunities of other students A3 submissions. We will also discuss the final project. It is important that you come to class! 12

13 Cone Trees [Robertson 91] Animated Transitions Polyarchy Visualization [Robertson 02] Degree-of-Interest Trees [Heer 04] Animate pivots across intersecting hierarchies. Tested a number of animation parameters. Best duration: ~1 sec Rotational movement degraded performance, translation preferred. Animation of expanding/collapsing branches 13

14 SpaceTree [Grosjean 04] Radial Graph Layout Break animated transitions into discrete stages Optimize animation to aid comprehension Animation in Radial Graph Layout Help maintain context of nodes and general orientation of user during refocus Transition Paths Linear interpolation of polar coordinates Node moves in an arc, not straight lines Moves along circle if not changing levels When changing levels, spirals to next ring Animation in Radial Graph Layout Transition constraints Minimize rotational travel (move former parent away from new focus in same orientation) Avoid cross-over of edges 14

15 Constraint: Retain Edge Orientation Constraint: Retain Neighbor Order NameVoyager [Wattenberg 04] Animated Transitions in Statistical Data Graphics 15

16 Log Transform Ordering / Sorting 16

17 Filtering 17

18 Timestep Month 1 Month 2 Change Encodings 18

19 Change Data Dimensions Change Data Dimensions Change Encodings + Axis Scaling 19

20 Data Graphics and Transitions Visual Encoding Transitions between Data Graphics? Change selected data dimensions or encodings Animation to communicate changes? During analysis and presentation it is common to transition between related data graphics. Can animation help? How does this impact perception? Principles for conveying information Congruence The structure and content of the external representation should correspond to the desired structure and content of the internal representation. Apprehension The structure and content of the external representation should be readily and accurately perceived and comprehended. [from Tversky 02] Principles for Animation Congruence Maintain valid data graphics during transitions Use consistent syntactic/semantic mappings Respect semantic correspondence Avoid ambiguity Apprehension Group similar transitions Minimize occlusion Maximize predictability Use simple transitions Use staging for complex transitions Make transitions as long as needed, but no longer 20

21 Principles for Animation Congruence Maintain valid data graphics during transitions Use consistent syntactic/semantic mappings Respect semantic correspondence Avoid ambiguity Apprehension Visual marks should Group similar transitions always represent the Minimize occlusion same data tuple. Maximize predictability Use simple transitions Use staging for complex transitions Make transitions as long as needed, but no longer Principles for Animation Congruence Maintain valid data graphics during transitions Use consistent syntactic/semantic mappings Respect semantic correspondence Avoid ambiguity Apprehension Different operators Group similar transitions should have distinct Minimize occlusion animations. Maximize predictability Use simple transitions Use staging for complex transitions Make transitions as long as needed, but no longer Principles for Animation Congruence Maintain valid data graphics during transitions Use consistent syntactic/semantic mappings Respect semantic correspondence Avoid ambiguity Apprehension Objects are harder Group similar transitions to track when Minimize occlusion occluded. Maximize predictability Use simple transitions Use staging for complex transitions Make transitions as long as needed, but no longer Principles for Animation Congruence Maintain valid data graphics during transitions Use consistent syntactic/semantic mappings Respect semantic correspondence Avoid ambiguity Apprehension Keep animation as Group similar transitions simple as possible. If Minimize occlusion complicated, break Maximize predictability into simple stages. Use simple transitions Use staging for complex transitions Make transitions as long as needed, but no longer 21

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23 How does animation affect perception? Conducted 2 controlled experiments 24 subjects (10 female), aged (M = 49.6) Business owners, educators, analysts, administrators Exp 1: Object Tracking (Syntactic Analysis) Measure object correspondence across transitions Exp 2: Value Change Estimation (Semantic Analysis) Measure graphical perception of changing values Experiment 1: Object Tracking Experimental Task Track 2 targets across a transition (then mask display) Click final positions of targets Dependent Variable Distance between clicks and targets 23

24 Experiment 1 Results: Animation Animated conditions outperform static Limited benefits for staging (except scatterplot) Duration constant; should stages be longer? Experiment 2: Change Estimation Experimental Task Follow 1 target across a transition (then mask display) Estimate percentage change in value (or Unknown) Dependent Variable Estimation error 24

25 Experiment 2 Results: Animation Subjective Preferences Animation more accurate (except Stacked Bars) Staged animation sig. worse in Donut Axis rescaling increases errors and? estimates Significant preference for animation. Staged animation was the most preferred, but not sig. for multi-stage timesteps in Stacked Bars and Donut Chart 25

26 Study Conclusions Appropriate animation improves graphical perception Simple transitions beat do one thing at a time Simple staging was preferred and showed benefits but timing important and in need of study Axis re-scaling hampers perception Avoid if possible (use common scale) Maintain landmarks better (delay fade out of lines) Subjects preferred animated transitions Animation in Trend Visualization Heer & Robertson study found that animated transitions are better than static transitions for estimating changing values. How does animation fare vs. static time-series depictions (as opposed to static transitions)? Experiments by Robertson et al, InfoVis 2008 Animated Scatterplot [Robertson 08] Traces [Robertson 08] 26

27 Study Analysis & Presentation Subjects asked comprehension questions. Presentation condition included narration. Multiples 10% more accurate than animation Presentation: Anim. 60% faster than multiples Analysis: Animation 82% slower than multiples User preferences favor animation Small Multiples [Robertson 08] Summary Animation is a salient visual phenomenon Attention, object constancy, causality, timing Design with care: congruence & apprehension For processes, static images may be preferable For transitions, animation has demonstrated benefits, but consider task and timing 27